[unreadable] The analysis of components in human breath is a powerful non-invasive technique for the diagnosis and monitoring of asthma, cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). The presence of elevated levels of nitric oxide (NO), carbon monoxide (CO), and ethane (C2H6) in the breath have been identified as biomarkers of these diseases, where nitric oxide and carbon monoxide are markers of airway inflammation and ethane is a marker of lipid peroxidation. The simultaneous quantification of these components of breath would be a powerful method to identify and differentiate lung diseases and their severity. Aerodyne Research, Inc. together with Harvard School of Pubic Health proposes to develop a fast response, compact, room temperature, quantum cascade laser based system for the quantitative analysis of multiple species in human breath by infrared absorption. In the Phase I study a novel room temperature cw laser will be characterized and its performance optimized for simultaneous nitric oxide and carbon dioxide monitoring in human breath. Detection limits of room temperature lasers for NO and C2H6 monitoring in a fast response system will be determined. A prototype instrument will be deployed in ongoing asthma studies collecting exhaled breath from human volunteers. These studies will answer key technical questions regarding the design of the instrument prior to more extensive Phase II studies. Relevance: The proposed breath analysis instrument will meet the need in the medical community for an instrument to allow the fast, noninvasive diagnosis and monitoring of patients with lung disease. It will also be a powerful research tool for investigating exposures that initiate and exacerbate asthma and COPD. [unreadable] [unreadable] [unreadable]